Double hang test.

[Disco]

Is there an article somewhere which explains the double hang test.

[asra]

Is there an article somewhere which explains the double hang test.

[Disco]

Thanks, that"s all i needed to know.Dean

[asra]

Something I would like clarified. There are a number of different methods for finding the center of mass. I take it this is at flying weight - pilot, half fuel, rotors. The center of mass I take it is the point on which the gyro will rotate end for end always ballanced and is the point the thrust line should pass through.The reason I am asking is I have just fitted a different motor to a gyro expecting the thrust line to be slightly high and it come in about 5" low. The thrust line is presently about shoulder height for seated pilot. 28" AK"s on single seater, thrust line is at approx center of mass of engine.Peter.

[asra]

Something I would like clarified. There are a number of different methods for finding the center of mass. I take it this is at flying weight - pilot, half fuel, rotors. Yes that right. The center of mass I take it is the point on which the gyro will rotate end for end always ballanced and is the point the thrust line should pass through. Yes thats also right.The reason I am asking is I have just fitted a different motor to a gyro expecting the thrust line to be slightly high and it come in about 5" low. The thrust line is presently about shoulder height for seated pilot. 28" AK"s on single seater, thrust line is at approx center of mass of engine.Peter.

Peter, if the engine is a Scooby doo then it represents a large portion of your AUW. If you then have a drop down offset gearbox it means mounting your motor even higher to acheive your prop keel clearance.This would raise your CofG in relation to your Thrustline.This is the reason both the GTG Kruza and Patrony 2 seater use a upward offset Autoflight. It helps to lowers the CofG and keep it close with your thrustline while still spinning a large prop.Regards SamL............

[asra]

Thanks Sam. The engine is a Suzuki K10a inline 4 with autoflight box turned up. Because the center of mass looked high I thought I had better check. Looks like I have got it right, though I will double check the ballances.

[Mark Horan]

something I never understand. How can the Ballance test line be determined by ballancing the gyro on its mains?Surely, this will only give the Gyro"s balance point in relation to the geometry of the landing gear.When the Gyro is in flight, the ballance point is affected by drag, airspeed and attitude, isnt it?If this is the case, then finding the CoG by ballancing on the mains will have no relationship to flying.Would it not also follow that the thrust line calculation would also be suspect. In My tandem, the thrust line looks to be high and when I have my fat guts in the front seat, one would expect a fulcrum action to occur that would lower the nose an make the thrust line really horrible, but the Machine flies really well. These are the reasons I am sus about the importance of Centre line thrustlook forward to ideas.Mark.mark.

[eigyro]

Mark, I think the need for the thrust line to be near the Vertical C of G is to prevent power-assisted forward rotationof the airframe if the rotor thrust/drag is removed in the event of a PIO or low-g turbulence event.I have no doubt someone here will correct me if I"m wrong.Cheers.

[Tim]

G"day Mark.When you balance the gyro on the mains you do so such that neither the nose wheel or the tail wheel have any weight on them. To do this you have to have the mains up on blocks because the angle is fairly nose high. The C of G then must fall somewhere on the vertical line up from the mains axles (if it didn"t the gyro would fall backwards or forwards. That only gives you one "line" which passes through the C of G. We then need to do another balance from a different perspective to get another "line" that passes through the C of G. The intersection point of these two lines is the Gyro C of G (or C of M). The C of G is the point about which all "free" bodies will rotate when acted upon by a force.Youn are right that the balance point is affected by such things as drag and airspeed.

[Tim]

Let me rephrase that last sentence. - The balance point itself is not affected by drag and airspeed, but rather the drag and airspeed affect the airframe reaction around the C of G.

[asra]

Mark, I"ve been sceptical of the CLT but tested this setup out of curiosity. I"ve still got to do more testing but I think it will come close to CLT with a full tank of fuel. The engine is very high compared to the seat tank and pilot. If you have a look on the Suzuki K10a thread there is a link to pictures of the engine Tim set up. Going off what I have found so far that machine with heavy blades would probabley be near CLT with a full tank of fuel depending on pilot weight. From what I can make out, if your machine will accelerate and decelerate at some point in the fuel load without pitching nose up or nose down, that will be CLT.

[tonydenton]

mark any chance of a photo of your gyro and what weight are you ?

[asra]

something I never understand. How can the Ballance test line be determined by ballancing the gyro on its mains?Surely, this will only give the Gyro"s balance point in relation to the geometry of the landing gear.When the Gyro is in flight, the ballance point is affected by drag, airspeed and attitude, isnt it?If this is the case, then finding the CoG by ballancing on the mains will have no relationship to flying.Would it not also follow that the thrust line calculation would also be suspect. In My tandem, the thrust line looks to be high and when I have my fat guts in the front seat, one would expect a fulcrum action to occur that would lower the nose an make the thrust line really horrible, but the Machine flies really well. These are the reasons I am sus about the importance of Centre line thrustlook forward to ideas.Mark.mark.Hi MarkAs Tim has already explained, Your machines CofG is the axis of all movement during flight. It is the point on your machine were pitch, roll and yaw occours. CofG is also known as Centre of Mass CofMDuring flight the only thing that can and will alter its position is the amount of fuel carried. Your CofG normally moves down as your machine burns off fuel. Conversly it will usually move up when you fill your tank to full. In order to find a happy medium, most people conduct these tests with half a tank of fuel. The balance and hang tests only give you your machines CofG. The next step is to superimpose the machines thrustline. The distance between your CofG and your Thrust line is your "Thrust Line Offset" There are 3 so called Gyroplane configurations.1) Low Thrust Line (LTL)2) Hight Trust Line (HTL)3) Centre Line Thrust (CLT)You must remember that all 3 Gyroplane configurations can be designed to fly as stable, easy and safe as the other. If your machine is correctly setup the the HTL design will still be stable in flight.In the photo above the YELLOW lines are the hang and balance test lines. The blue lines are reference lines, ie; KEEL reference (horizontal), and

[GraemeMonro]

Couple of questions Sam.In the pics above does it make any difference having the rotors tied, are you transfering any weight anywhere?Allan does not seem to be holding the joystick in a central position, will this alter anything?Just curious.Graeme.

[asra]

Couple of questions Sam.In the pics above does it make any difference having the rotors tied, are you transfering any weight anywhere?Allan does not seem to be holding the joystick in a central position, will this alter anything?Just curious.Graeme.G"Day GraemeThe position of the blades during the balance test dosnt matter. This is due to the blades being mounted at there CofG point. So if you lower and drop a blade, and raise the other, each ends up being an opposite but equal, so it makes no difference. The only time the stick needs to be locked is during the hang test. The best way to do this is by chocking the torque tube in its central position. The blades are not usually mounted during the hang test.Hope this helps.Regards SamL...........